Even though citizenship in the United States was not extended to American Indians as a whole by federal statute until the Citizenship Act of 1924, members of many Native tribes and nations had become citizens before that, usually after they accepted the legal terms of assimilation. Citizenship sometimes was part of treaty negotiations, as well as allotment legislation. Some individual American Indians were offered citizenship for service in the U.S. armed forces, even as others were denied the right to vote by some federal courts. An American Indian woman could become a citizen by marrying a man who held citizenship status (but not vice versa). Despite the existence of some open doors, the opportunity of acquiring citizenship via naturalization, as provided to immigrants from abroad, was denied to Indians living in the United States.

An offer of citizenship to members of Native nations usually included destruction of their collective government and land base. Treaties in 1855 and 1862 involving the Wyandots (Hurons) and Ottawas, for example, required the Indians to relinquish their collective identity in return for U.S. citizenship and individual land ownership. A series of treaties in the 1860s gave the president and the courts the power to determine when adult male allottees had become sufficiently "intelligent and prudent" to conduct their affairs and interests. The treaty of 1867 with the Potawatomies permitted women who were heads of families or single adult women to become citizens in the same manner as males, and authorized the Tribal Business Committee and the agent to determine the competency of Indians to manage their own affairs (ORACLE, n. d.)

Citizenship "was a move by the federal government to absorb Indians into the mainstream of American life. No doubt Indian participation in World War I accelerated the granting of citizenship to all Indians, but it seems more likely to have been the logical extension and culmination of the assimilation policy" (Nebraska Studies, n.d.). To this day, some Native Americans reject the rights of U.S. citizenship (such as voting) as a sign of colonialism. A few have refused to pay taxes and have found themselves prosecuted for this action by the Internal Revenue Service.

Some Native Americans have contended that citizenship would erode their peoples' distinct status as sovereign nations. In the words of one observer, "United States citizenship was just another way of absorbing us and destroying our customs and our government. How could these Europeans come over and tell us we were citizens in our country? We had our own citizenship. By its [the Citizenship Act of 1924] provisions all Indians were automatically made United States citizens whether they wanted to be so or not. This was a violation of our sovereignty" (Nebraska Studies, n.d.).

Charles Curtis (1860–1936), of Kansa and Osage heritage, was one of the most prominent advocates of citizenship as a method of assimilation. The first American Indian to do so, Curtis served as a Republican member of the U.S. Senate from 1907 to 1913 and again from 1915 to 1929. Curtis rose to majority leader (1924–1929) and served as Herbert Hoover's vice president (1929–1933). As chairman of the Senate Committee on Indian Affairs in 1924, Curtis sponsored the Indian Citizenship Act.

As allotment and its provisions for citizenship were being legislated, the Supreme Court denied citizenship to Indians who wished to take the policy to its logical conclusion. In 1884, in Elk v. Wilkins, Indians were denied the right to vote despite the wording of the recently passed Fourteenth Amendment to the U.S. Constitution. The U.S. Supreme Court held in Elk v. Wilkins that an Indian is not made a citizen by the Fourteenth Amendment. This position held even if the Indian is living apart from his nation or band. The court also ruled that acts of Congress do not generally apply to Indians unless they are specifically mentioned.

At issue was the constitutional status of American Indians for purposes of citizenship and voting. The Fourteenth Amendment granted citizenship to "all persons born or naturalized in the United States, and subject to the jurisdiction of the United States." Did American Indians fall under this definition? A federal district court ruled that it did not apply to Indians who had not been "born subject to its jurisdiction—that is, in its power and obedience" (McKay v. Campbell 16 Fed. Cas. 161 [1871] [No. 8840]).

For instance, John Elk had been born outside U.S. jurisdiction, but moved to Omaha as an adult and lived what the court described as a "civilized" life. He sought to become a citizen and exercise the right to vote in Omaha elections during 1880. The Supreme Court ruled that the Fifteenth Amendment (which grants the right to vote to all persons regardless of race) did not apply in Elk's case, because he was not born in an area under U.S. jurisdiction. Therefore, Elk was not a citizen within the meaning of the Fourteenth Amendment. The fact that Elk had abandoned his Indian relatives and lifeways did not matter to the court. Elk's citizenship and voting rights were denied because the court held that an affirmative act was required of the United States before an Indian could become a citizen. The Supreme Court's opinion cited a dozen treaties, four court rulings, four laws, and eight opinions of the U.S. attorney general requiring "proof of fitness for civilization" as a precondition of granting Indians citizenship and voting rights.

Six years after John Elk's desire for citizenship was denied, Congress passed the Indian Territory Naturalization Act (26 Stat. 81, 99–100), which allowed any Indian living in Indian Territory to apply for citizenship through the federal courts. The aim of this Act was to break down communal loyalties among Native Americans in Indian Territory as it moved toward statehood as Oklahoma.

Vine Deloria, Jr., commented on Elk v. Wilkins: "Thus, while federal courts were busy maintaining the plenary power of Congress over Indians, and classifying Indian tribes as wards of the federal government, and denying an international dimension to Indian political existence, the individual Indians seeking to exercise their constitutional rights were being told that they were, in effect, no more than the children of [foreign] subjects" (Deloria, 1985, 146–147).